This invention relates to improvements in immunotherapy techniques for treating extrinsic asthma. More particularly, it relates to an immunotherapy technique for decreasing the bronchial sensitivity to cat dander of individuals suffering from cat-induced asthma.
Extrinsic asthma is an atopic allergic disease induced in susceptible individuals by exposure to certain environmental antigens, called allergens. The disease is characterized by breathing difficulties, wheezing, coughing, and tightness of the chest. Recently, it has been determined that a significant number of extrinsic asthmatics are sensitive to cat dander, and that this form of the disease is particularly severe. It has been reported, for example, that out of 1000 asthmatic children tested by bronchial challenge with dander extracts, 43% were positive. Of 300 consecutive patients with asthma or rhinitis (or both) seen at the Massachusetts General Hospital Allergy Clinic, 82 patients (27%) were aware of symptoms following exposure to cat. Further, it has recently been shown that patients suffering from cat sensitivity are statistically more likely to exhibit the more troublesome asthma symptoms as opposed to those of rhinitis or conjunctivitis.
The treatment of choice for extrinsic asthma is avoidance of the allergen or allergen carrying substance which induces the symptoms. For accidental exposures, or where avoidance is impossible, drugs such as epinephrine, aminophylline, and certain steroids are administered to control the allergic reaction. Asthma as well as other atopic diseases such as rhinitis and conjunctivitis, are sometimes treated with immunotherapy. Immunotherapy refers to the practice of administering extracts of the allergy producing material to an allergic patient in gradually increasing amounts. It can often "desensitize" or "hyposensitize" the patient, i.e., render him less sensitive or less allergic to the allergens used.
Convincing proof that immunotherapy is effective for treating any atopic disease was unavailable until quite recently. Historically, grave doubts have been expressed concerning the utility of the entire approach. However, in the last 20 years, convincing evidence backed up by double-blind studies has demonstrated, at least with respect to immunotherapy directed to the treatment of ragweed induced rhinitis, that this technique can be useful in treating certain patients.
Reports on the effectiveness of attempts to "desensitize" or "hyposensitize" allergic patients to exposure to cat dander have been mixed. For example, Tuft, et al., (Am. J. Med. Sci., V. 253, p. 49, 1967) report that treatment of 18 cat dander sensitive patients (number with asthma unspecified) with alum precipitated pyridine cat dander extracts resulted in significant improvement in the tolerance of most patients to cat exposure. In Annals of Allergy, (Vol. 36, p. 165, March 1976), Tuft, et al. report that hyposensitization with certain unstandardized animal dander extracts can bring about improved tolerance in a sizeable percentage of patients, and compares favorably with that obtained from pollen therapy in hay fever patients. Asthma symptoms were not studied separately. In contrast, Brown, et al., (Annals of Allergy, Vol. 26, p. 305, June 1968) report that attempts at hyposensitization with either unstandardized pyridine or aqueous dander extracts resulted in an insignificant number of improved asthma cases.
The material used for immunotherapy has typically been a crude soluble extract of the allergen bearing agent. For example, in the above noted studies, the extracts employed consisted of the alum precipitated pyridine fraction or the water soluble fraction of cat epithelium. The active allergen content of crude animal epithelial extracts has been unknown and unstandardized, and no controlled studies of immunotherapy in animal dander allergy are available. In fact, the previous reports of immunotherapy directed to animal dander sensitivity are difficult or impossible to evaluate in view of the uncertain qualities of the extracts used. Purified allergens have been used in immunotherapy. See, for example, A Single Year of Immunotherapy for Ragweed Hay Fever, Annals of Internal Medicine, Volume 75, No. 5, p. 663, Lichtenstein, et al. However, with purified allergens it is often impossible to know whether all or even most of the relevant allergen content present in the crude material has been included.
Immunotherapy directed to asthma has been reviewed in Asthma, K. F. Austen, et al., Academic Press, 1973, p. 211.